build(deps): bump gatsby-remark-images from 3.6.0 to 3.8.1 in /docs (#1601)

Bumps [gatsby-remark-images](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-remark-images) from 3.6.0 to 3.8.1.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/[email protected]/packages/gatsby-remark-images/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/[email protected]/packages/gatsby-remark-images)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]